U.S. patent application number 10/809352 was filed with the patent office on 2004-10-28 for magnetic disk and method of manufacturing same.
This patent application is currently assigned to HOYA CORPORATION. Invention is credited to Ishiyama, Masafumi, Shimokawa, Koichi.
Application Number | 20040213951 10/809352 |
Document ID | / |
Family ID | 32852757 |
Filed Date | 2004-10-28 |
United States Patent
Application |
20040213951 |
Kind Code |
A1 |
Shimokawa, Koichi ; et
al. |
October 28, 2004 |
Magnetic disk and method of manufacturing same
Abstract
Disclosed is a method of manufacturing magnetic disks,
comprising a magnetic layer, a protective layer, and a lubricating
layer on a substrate. In the process, a lubricant alpha comprising
a compound denoted by chemical formula
HO--CH.sub.2--CH(OH)--CH.sub.2--O--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)-
p-(O--CF2)q--O--CF.sub.2--CH.sub.2--O--CH.sub.2--CH(OH)--CH.sub.2--OH
wherein p and q are natural number, and a compound denoted by
chemical formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF.sub.2)n--O--CF.sub.2---
CH.sub.2--OH wherein m and n are natural number, is fractionated by
molecular weight to prepare a lubricant a having a weight average
molecular weight (Mw) of from 3,000 to 7,000 and a molecular weight
dispersion of less than or equal to 1.2; a lubricant beta
comprising a compound denoted by the chemical formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF2)n--O--CF.sub.2--CH.su-
b.2--OH wherein m and n are natural number, is fractionated by
molecular weight to prepare a lubricant b having a weight average
molecular weight (Mw) of from 2,000 to 5,000 and a molecular weight
dispersion of less than or equal to 1.2; a lubricant c comprising a
mixture of lubricants a and b is prepared; and a film of lubricant
c is formed on a protective layer provided on a substrate to form a
lubricating layer. A magnetic disk comprising a magnetic layer, a
protective layer, and a lubricating layer on a substrate, in which
the lubricating layer has been formed on the protective layer is
also enclosed.
Inventors: |
Shimokawa, Koichi;
(Yamanashi, JP) ; Ishiyama, Masafumi; (Singapore,
SG) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN, P.L.C.
1950 ROLAND CLARKE PLACE
RESTON
VA
20191
US
|
Assignee: |
HOYA CORPORATION
Tokyo
JP
HOYA MAGNETICS SINGAPORE PTE. LTD.
Singapore
SG
|
Family ID: |
32852757 |
Appl. No.: |
10/809352 |
Filed: |
March 26, 2004 |
Current U.S.
Class: |
428/65.8 ;
428/835.8; 428/841.3; G9B/5.281; G9B/5.3 |
Current CPC
Class: |
G11B 5/7257 20200801;
C10N 2070/00 20130101; C10M 171/04 20130101; G11B 5/725 20130101;
C10N 2050/02 20130101; C10M 2211/0425 20130101; C10M 107/38
20130101; C10N 2020/04 20130101; G11B 5/8408 20130101; C10M
2213/043 20130101; C10N 2040/18 20130101; C10M 2211/0425 20130101;
C10M 2211/0425 20130101; C10M 2213/043 20130101; C10M 2213/043
20130101 |
Class at
Publication: |
428/065.8 ;
428/694.0BF |
International
Class: |
B32B 003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2003 |
JP |
2003-96820 |
Oct 22, 2003 |
JP |
2003-361982 |
Claims
1. A method of manufacturing magnetic disks comprising a magnetic
layer, a protective layer, and a lubricating layer on a substrate,
in which a lubricant alpha comprising a compound denoted by
chemical formula
HO--CH.sub.2--CH(OH)--CH.sub.2--O--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4-
)p-(O--CF2)q--O--CF.sub.2--CH.sub.2--O--CH.sub.2--CH(OH)--CH.sub.2--OH
[Chem. 1]wherein p and q are natural number, and a compound denoted
by chemical formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF2)n---
O--CF.sub.2--CH.sub.2--OH [Chem. 2]wherein m and n are natural
number, is fractionated by molecular weight to prepare a lubricant
a having a weight average molecular weight (Mw) of from 3,000 to
7,000 and a molecular weight dispersion of less than or equal to
1.2; a lubricant beta comprising a compound denoted by the chemical
formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF.sub.2)n--O--CF.sub.2--
-CH.sub.2--OH [Chem. 3]wherein m and n are natural number, is
fractionated by molecular weight to prepare a lubricant b having a
weight average molecular weight (Mw) of from 2,000 to 5,000 and a
molecular weight dispersion of less than or equal to 1.2; a
lubricant c comprising a mixture of lubricants a and b is prepared;
and a film of lubricant c is formed on a protective layer provided
on a substrate to form a lubricating layer.
2. The method of manufacturing magnetic disks of claim 1, wherein
the fractionation by molecular weight is conducted by supercritical
extraction.
3. The method of manufacturing magnetic disks of claim 1 wherein
lubricant c is prepared by obtaining a composition A of lubricant a
dispersed in a fluorine-base solvent, obtaining a composition B of
lubricant b dispersed in a fluorine-base solvent, mixing
compositions A and B, and extracting lubricant c from the mixed
composition.
4. The method of manufacturing magnetic disks of claim 1 wherein
after forming the lubricating layer, the resultant magnetic disk is
exposed to an atmosphere of from 50 to 150.degree. C. to adhere
lubricant c to the protective layer.
5. The method of manufacturing magnetic disks of claim 1 wherein
the protective layer is formed by plasma CVD.
6. The method of manufacturing magnetic disks of claim 1 employed
for load-unload system magnetic disk devices.
7. The method of manufacturing magnetic disks of claim 1 wherein
Fomblin Ztetraol (product name) made by Solvay Solexis is selected
as lubricant alpha and Fomblin Zdol (product name) made by Solvay
Solexis is selected as lubricant beta.
8. A magnetic disk comprising a magnetic layer, a protective layer,
and a lubricating layer on a substrate, in which the lubricating
layer has been formed on the protective layer, said lubricating
layer being comprised of a lubricant c, comprising a lubricant a
having a weight average molecular weight (Mw) of from 3,000 to
7,000 and a molecular weight dispersion of less than or equal to
1.2 obtained by refining a lubricant alpha comprising the compound
denoted by the chemical formula
HO--CH.sub.2--CH(OH)--CH.sub.2--O--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4-
)p-(O--CF2)q--O--CF.sub.2--CH.sub.2--O--CH.sub.2--CH(OH)--CH.sub.2--OH
[Chem. 4]wherein p and q are natural number, and a compound denoted
by chemical formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF2)n---
O--CF.sub.2--CH.sub.2--OH [Chem. 5]wherein m and n are natural
number, and a lubricant b having a weight average molecular weight
(Mw) of from 2,000 to 5,000 and a molecular weight dispersion of
less than or equal to 1.2, comprising a lubricant beta comprising a
compound denoted by chemical formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF2)n---
O--CF.sub.2--CH.sub.2--OH [Chem. 6]. wherein m and n are natural
number.
9. A magnetic disk comprising a magnetic layer, a protective layer,
and a lubricating layer on a substrate, in which the lubricating
layer has been formed on the protective layer, said lubricating
layer comprising a compound denoted by the chemical formula
HO--CH.sub.2--CH(OH)--CH.sub.2---
O--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)p-(O--CF2)q--O--CF.sub.2--CH.sub-
.2--O--CH.sub.2--CH(OH)--CH.sub.2--OH [Chem. 7]wherein p and q are
natural number, and a compound denoted by the chemical formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF2)n--O--CF.sub.2--CH.s-
ub.2--OH [Chem. 8]wherein m and n are natural number, and the
lubricating layer contains --COOH atomic groups detectable by time
of flight secondary ion mass spectrometry.
10. A magnetic disk comprising a magnetic layer, a protective
layer, and a lubricating layer on a substrate, in which the
lubricating layer comprises: a compound denoted by the chemical
formula
HO--CH.sub.2--CH(OH)--CH.sub.2--O--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4-
)p-(O--CF2)q--O--CF.sub.2--CH.sub.2--O--CH.sub.2--CH(OH)--CH.sub.2--OH
[Chem. 9]wherein p and q are natural number, a compound denoted by
the chemical formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF2)n---
O--CF.sub.2--CH.sub.2--OH [Chem. 10]wherein m and n are natural
number, and a compound having in its molecular structure --COOH
atomic group detectable by time of flight secondary ion mass
spectrometry.
11. The magnetic disk of claim 8 wherein the protective layer is a
carbon-base protective layer.
12. The magnetic disk of claim 9, wherein the protective layer is a
carbon-base protective layer.
13. The magnetic disk of claim 10, wherein the protective layer is
a carbon-base protective layer.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of manufacturing
magnetic disks to be loaded into magnetic disk devices such as hard
disk drives, as well as to magnetic disks.
BACKGROUND TECHNOLOGY
[0002] In magnetic disk devices such as hard disk drives (HDDs), a
contact start and stop (CSS) system is employed in which a magnetic
head is brought into contact with a contact slide area (CSS area)
located in the inner-circumferential area of the magnetic disk
surface when stopped, and the magnetic head flies upward while
sliding in contact with the disk surface in the CSS area and then
recording or reproduction is conducted in a disk area surface for
recording and reproduction that is located to the outside of the
CSS area when activated. When an operation has been completed, the
magnetic head is withdrawn from the recording and reproduction area
into the CSS area, after which the magnetic head descends while
sliding in contact with the disk surface in the CSS area and comes
to a stop. In the CSS system, the operations of starting and
terminating in which sliding contact occurs are called CSS
operations.
[0003] In a magnetic disk employing the CSS system, it is necessary
to provide both a CSS area and a recording and reproduction area on
the disk surface. It is also necessary to provide an uneven
topography having a certain surface roughness on the magnetic disk
surface so that the magnetic head and magnetic disk do not adhere
to each other when in contact.
[0004] To reduce the damage caused by the magnetic head sliding in
contact with the magnetic disk during CSS operations, a magnetic
recording medium in which a coating of a perfluoroalkylpolyether
lubricant of the structure
HOCH.sub.2--CF.sub.2O--(C.sub.2F.sub.4O).sub.p--(CF.sub.2O).sub-
.q--CH.sub.2OH is applied is known, for example, through Japanese
Unexamined Patent Publication (KOKAI) Showa No. 62-66417 (Patent
Reference 1).
[0005] Similarly, magnetic recording media of high CSS durability
are known through Japanese Unexamined Patent Publications (KOKAI)
Heisei No. 9-282642 (Patent Reference 2) and Heisei No. 10-143838
(Patent Reference 3).
[0006] Recently, magnetic disk devices based on the load-unload
(LUL) system have been introduced as substitutes for the CSS
system. In the LUL system, the magnetic head is withdrawn to an
inclined base, called a "ramp", positioned beyond the disk when
stopped. When activated, the magnetic disk is caused to rotate,
after which the magnetic head slides over the magnetic disk from
the ramp to conduct recording and reproduction. This series of
operations is referred to as LUL operations. Since a broader
recording and reproduction area can be ensured on the magnetic disk
surface than in the CSS system, the LUL system is desirable for
achieving high information capacity. Further, since the uneven
topography employed in the CSS system is not required on the
magnetic disk surface, the magnetic disk surface can be made
extremely smooth. This permits a significant decrease in the flying
height level of the magnetic head, making it possible to achieve
high S/N ratios for recording signals.
[0007] With the introduction of the LUL system, as the magnetic
head flying height level has decreased sharply in discontinuous
fashion, the requirement that a magnetic disk stably operate even
at an extremely low flying height level of 10 nm or less has
emerged. However, when the magnetic head is moved rapidly while
flying over the surface of the magnetic disk at an extremely low
level, there are problems in that "fly-sticking" impairment and
head corrosion impairment frequently occur.
[0008] "Fly-sticking" impairment refers to impairment in the form
of modulation in the position and flying level of the magnetic head
during flying. It is accompanied by irregular reproduction output.
In some cases, the magnetic disk contacts the magnetic head during
flying, causing the head to crash and damaging the magnetic
disk.
[0009] "Corrosion" impairment refers to impairment in the form of
the corrosion of elements of the magnetic head that creates
problems during recording and reproduction, and in some causes,
renders recording and reproduction impossible. The corroded
elements sometimes expand, damaging the surface of the magnetic
disk during flying.
[0010] Recently, the rotational speed of the magnetic disk has been
increased to enhance the response time of the magnetic disk device.
The rotational speed of 2.5-inch magnetic disk devices of small
diameter suited to mobile applications was formerly 4,200 rpm, but
has recently been increased to 5,400 rpm and above to enhance
response characteristics.
[0011] When the magnetic disk is rotated at such high speeds, a
phenomenon occurs in which the centrifugal force accompanying
movement causes the lubricating layer to migrate, resulting in
nonuniformity of the thickness of the lubricating layer within the
magnetic disk surface.
[0012] When the thickness of the lubricating layer is increased on
the outer circumference portion of the disk, fly-sticking
impairment and head crashing impairment tend to occur when the
magnetic head enters from the outer circumferential portion of the
disk during an LUL operation. When the thickness of the lubricating
layer is reduced on the inner circumferential portion, the
reduction in lubricating performance tends to cause head
crashing.
[0013] The lubricating techniques described in above-cited Patent
References 1, 2, and 3 that have been employed thus far were
primarily developed with emphasis on improving CSS operations. When
they are employed in LUL-system magnetic disks, the frequency of
the above-described impairments is high, and it is already
difficult to satisfy the reliability that has recently come to be
required of magnetic disks. Thus, they have become factors impeding
the development of high-capacity, high S/N ratio, rapid-response
LUL-system magnetic disks.
[0014] Based on such problems, the present invention has for its
object to provide a magnetic disk, particularly a load-unload
magnetic disk, equipped with a highly adhesive lubricating layer
that is capable of preventing migration even at high rotational
speeds of 5,400 rpms and above and that is capable of preventing
fly-sticking and corrosion impairment even at extremely low flying
levels of 10 nm or less, for example.
DISCLOSURE OF THE INVENTION
[0015] The present inventors discovered that the above-stated
problems were solved by the inventions set forth below; the present
invention was devised on that basis.
[0016] The present invention relates to:
[0017] (1) A method of manufacturing magnetic disks comprising a
magnetic layer, a protective layer, and a lubricating layer on a
substrate, in which
[0018] a lubricant alpha comprising a compound denoted by chemical
formula
HO--CH.sub.2--CH(OH)--CH.sub.2--O--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)-
p-(O--CF2)q--O--CF.sub.2--CH.sub.2--O--CH.sub.2--CH(OH)--CH.sub.2--OH
[Chem. 1]
[0019] wherein p and q are natural number,
[0020] and a compound denoted by chemical formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF2)n--O--CF.sub.2--CH.su-
b.2--OH [Chem. 2]
[0021] wherein m and n are natural number,
[0022] is fractionated by molecular weight to prepare a lubricant a
having a weight average molecular weight (Mw) of from 3,000 to
7,000 and a molecular weight dispersion of less than or equal to
1.2;
[0023] a lubricant beta comprising a compound denoted by the
chemical formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF2)n--O--CF.sub.2--CH.su-
b.2--OH [Chem. 3]
[0024] wherein m and n are natural number,
[0025] is fractionated by molecular weight to prepare a lubricant b
having a weight average molecular weight (Mw) of from 2,000 to
5,000 and a molecular weight dispersion of less than or equal to
1.2;
[0026] a lubricant c comprising a mixture of lubricants a and b is
prepared; and
[0027] a film of lubricant c is formed on a protective layer
provided on a substrate to form a lubricating layer.
[0028] (2) The method of manufacturing magnetic disks of (1) above
wherein the fractionation by molecular weight is conducted by
supercritical extraction.
[0029] (3) The method of manufacturing magnetic disks of (1) or (2)
above wherein lubricant c is prepared by obtaining a composition A
of lubricant a dispersed in a fluorine-base solvent, obtaining a
composition B of lubricant b dispersed in a fluorine-base solvent,
mixing compositions A and B, and extracting lubricant c from the
mixed composition.
[0030] (4) The method of manufacturing magnetic disks of any of
from (1) to (3) above wherein after forming the lubricating layer,
the resultant magnetic disk is exposed to an atmosphere of from 50
to 150.degree. C. to adhere lubricant c to the protective
layer.
[0031] (5) The method of manufacturing magnetic disks of any of
from (1) to (4) above wherein the protective layer is formed by
plasma CVD.
[0032] (6) The method of manufacturing magnetic disks of any of
from (1) to (5) above employed for load-unload system magnetic disk
devices.
[0033] (7) The method of manufacturing magnetic disks of any of
from (1) to (6) above further characterized in that Fomblin
Ztetraol (product name) made by Solvay Solexis is selected as
lubricant alpha and Fomblin Zdol (product name) made by Solvay
Solexis is selected as lubricant beta.
[0034] (8) A magnetic disk comprising a magnetic layer, a
protective layer, and a lubricating layer on a substrate, in which
the lubricating layer has been formed on the protective layer, said
lubricating layer being comprised of a lubricant c,
[0035] comprising a lubricant a having a weight average molecular
weight (Mw) of from 3,000 to 7,000 and a molecular weight
dispersion of less than or equal to 1.2 obtained by refining a
lubricant alpha comprising the compound denoted by the chemical
formula
HO--CH.sub.2--CH(OH)--CH.sub.2--O--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)-
p-(O--CF2)q--O--CF.sub.2--CH.sub.2--O--CH.sub.2--CH(OH)--CH.sub.2--OH
[Chem. 4]
[0036] wherein p and q are natural number,
[0037] and a compound denoted by chemical formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF2)n--O--CF.sub.2--CH.su-
b.2--OH [Chem. 5]
[0038] wherein m and n are natural number,
[0039] and a lubricant b having a weight average molecular weight
(Mw) of from 2,000 to 5,000 and a molecular weight dispersion of
less than or equal to 1.2, comprising a lubricant beta comprising a
compound denoted by chemical formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF2)n--O--CF.sub.2--CH.su-
b.2--OH [Chem. 6].
[0040] wherein m and n are natural number.
[0041] (9) A magnetic disk comprising a magnetic layer, a
protective layer, and a lubricating layer on a substrate, in
which
[0042] the lubricating layer has been formed on the protective
layer, said lubricating layer comprising a compound denoted by the
chemical formula
HO--CH.sub.2--CH(OH)--CH.sub.2--O--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)-
p-(O--CF2)q--O--CF.sub.2--CH.sub.2--O--CH.sub.2--CH(OH)--CH.sub.2--OH
[Chem. 7]
[0043] wherein p and q are natural number,
[0044] and a compound denoted by the chemical formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF2)n--O--CF.sub.2--CH.su-
b.2--OH [Chem. 8]
[0045] wherein m and n are natural number,
[0046] and the lubricating layer contains --COOH atomic groups
detectable by time of flight secondary ion mass spectrometry.
[0047] (10) A magnetic disk comprising a magnetic layer, a
protective layer, and a lubricating layer on a substrate, in which
the lubricating layer comprises:
[0048] a compound denoted by the chemical formula
HO--CH.sub.2--CH(OH)--CH.sub.2--O--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)-
p-(O--CF2)q--O--CF.sub.2--CH.sub.2--O--CH.sub.2--CH(OH)--CH.sub.2--OH
[Chem. 9]
[0049] wherein p and q are natural number,
[0050] a compound denoted by the chemical formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF2)n--O--CF.sub.2--CH.su-
b.2--OH [Chem. 10]
[0051] wherein m and n are natural number,
[0052] and a compound having in its molecular structure --COOH
atomic group detectable by time of flight secondary ion mass
spectrometry.
[0053] (11) The magnetic disk of any of (8) to (10) above, wherein
the protective layer is a carbon-base protective layer.
BRIEF DESCRIPTION OF DRAWINGS
[0054] FIG. 1 is a sectional view of a typical embodiment of the
magnetic disk of the present invention. In the figure, 10 denotes a
magnetic disk, 1 denotes a disk substrate, 2 denotes a base layer,
3 denotes a magnetic layer, 4 denotes a protective layer, and 5
denotes a lubricating layer.
[0055] The present inventors studied the above-described
impairments of magnetic disks, which have recently become marked,
to achieve the above-stated goal, discovering that the following
mechanism produces the following results.
[0056] They discovered that, when the low flying height level of
the magnetic head reaches 10 nm or less, the magnetic head
repeatedly causes the lubricating layer on the surface of the
magnetic disk to undergo adiabatic compression and adiabatic
expansion through air molecules during flying, thereby causing the
lubricating layer to tend to repeatedly undergo heating and
cooling. They also discovered that this tends to promote breaking
down of the lubricant comprising the lubricating layer into lower
molecules.
[0057] When the lubricant breaks down into lower molecules,
fluidity increases and adhesion to the protective layer decreases.
The highly fluid lubricant was observed to transfer to and deposit
on the magnetic head, positioned nearby, destabilizing the flying
position and causing fly-sticking impairment.
[0058] In particular, in magnetic heads with NPAB (negative
pressure air bearing surface) sliders that have recently been
introduced, the lubricant tends to be sucked off by the strong
negative pressure generated beneath the magnetic head, which is
thought to exacerbate the transfer deposition phenomenon.
[0059] The transferred lubricant sometimes produces acids such as
hydrofluoric acid, in some cases corroding the element of the
magnetic head. Heads containing magnetic resistance-effect elements
are particularly prone to corrosion.
[0060] The present inventors discovered that the LUL system
exacerbates these impairments. In LUL systems, as opposed to CSS
systems, the magnetic head does not slide in contact over the
magnetic disk surface. Thus, lubricant that has been transferred to
and deposited on the magnetic head tends not to transfer to the
magnetic disk side. In a conventional CSS system, lubricant that
has transferred to the magnetic head tends to be cleaned away by
sliding in contact with the CSS area of the magnetic disk, which
would explain why such impairments are not marked.
[0061] Based on these research results, the present inventors
continued their study in light of the above-stated goal. As a
result of continuous investigation based on trial and error with
numerous lubricants, they devised the present invention.
[0062] Fomblin Ztetraol (product name), an alcohol-modified
perfluoropolyether-base lubricant made by Solvay Solexis, is
thought to contain alcohol-modified perfluoropolyether compounds
having various terminal group structures, such as monool compounds,
diol compounds, triol compounds, and tetraol compounds. Solvay
Solexis clearly states that Fomblin Ztetraol contains the compound
denoted by the chemical formula
HO--CH.sub.2--CH(OH)--CH.sub.2--O--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)-
p-(O--CF2)q--O--CF.sub.2--CH.sub.2--O--CH.sub.2--CH(OH)--CH.sub.2--OH
[Chem. 11]
[0063] wherein p and q are natural number,
[0064] (referred to hereinafter as perfluorotetraol compound), but
analysis by the present inventors revealed that at least the
compound denoted by the chemical formula
HO--CH.sub.2--CF.sub.2(--O--C.sub.2F.sub.4)m-(O--CF.sub.2)n--O--CF.sub.2---
CH.sub.2--OH [Chem. 12]
[0065] wherein m and n are natural number,
[0066] (referred to hereinafter as perfluorodiol compound) is also
contained.
[0067] That is, when the above Fomblin Ztetraol was analyzed by
nuclear magnetic resonance (NMR) or time of flight secondary ion
mass spectrometry (TOF-SIMS), the above perfluorotetraol compound
was found to be the primary compound, but the above perfluorodiol
compound was found to be present in a content of from 10 to 30
molar percent as another principal component. Other compounds are
also thought to be present as impurities in quantities of about the
limit of detection.
[0068] Fomblin Zdol (product name) made by Solvay Solexis, also an
alcohol-modified perfluoropolyether-base lubricant made by Solvay
Solexis, is also clearly stated by Solvay Solexis to contain the
above perfluorodiol compound. Upon analysis by the present
inventors, this perfluorodiol was found to be the primary
component. Other compounds are also thought to be present as
impurities in quantities of about the limit of detection.
[0069] In alcohol-modified perfluoropolyether-base lubricants,
based on the degree of modification by alcohol, that is, based on
the difference in the number of hydroxyl groups bonded to the
terminal group of the perfluoropolyether main chain, the
lubricating properties and adhesive strength of the lubricant
molecules vary.
[0070] Accordingly, based on the content and generation of various
alcohol-modified compounds such as monool compounds, diol
compounds, triol compounds, and tetraol compounds, the
characteristics of the lubricant vary widely.
[0071] In the present invention, a lubricant (referred to as
lubricant a) is refined to a specified molecular weight
distribution by fractionating by molecular weight a lubricant alpha
containing primary components in the form of the above
perfluorotetraol compound and perfluorodiol compound. Further, a
lubricant (referred to as lubricant b) is refined to a specified
molecular weight distribution by fractionating by molecular weight
a lubricant beta containing a primary component in the form of the
above perfluorodiol compound. A mixed lubricant (referred to as
lubricant c) is prepared by mixing lubricants a and b. A film of
lubricant c is then coated on the protective layer to solve the
above-stated problems.
[0072] The content of the perfluorodiol compound in lubricant alpha
is desirably from 10 to 30 molar percent.
[0073] Although the mechanism by which the above-stated problems
are solved in the present invention is not necessarily clear,
fractionation is thought to control the state of the
alcohol-modified perfluoropolyether compounds contained in
lubricants alpha and beta.
[0074] When fractionation is conducted so that the molecular weight
distribution achieved in lubricant a is a weight average molecular
weight (Mw) of 3,000 to 7,000 and so that the molecular weight
dispersion when denoted as the weight average molecular weight
(Mw)/the number average molecular weight (Mn) is less than or equal
to 1.2, the content ratio of the above perfluorodiol compounds, for
example, is thought to be increased.
[0075] When fractionation is conducted so that the molecular weight
distribution achieved in lubricant b is a weight average molecular
weight (Mw) of 2,000 to 5,000 and so that the molecular weight
dispersion when denoted as the weight average molecular weight
(Mw)/the number average molecular weight (Mn) is less than or equal
to 1.2, the content ratio of the above perfluorodiol compounds, for
example, is thought to be reduced.
[0076] Mixing the two fractionated lubricants (to obtain lubricant
c) is thought to achieve a content status of the various compounds,
that is, a content status (ratio and status of products generated
by mixing) of the above perfluorotetraol compounds and
perfluorodiol compounds, that is desirable for solving the above
stated problems.
[0077] An example of a desirable lubricant alpha in the present
invention is Fomblin Ztetraol (product name) made by Solvay
Solexis. An example of a desirable lubricant beta is Fomblin Zdol
(product name) made by Solvay Solexis. In Japan, both are sold by
Solvay Solexis Co., Ltd.
[0078] The present invention provides a magnetic disk having a
magnetic layer, protective layer, and lubricating layer on a
substrate. That is, it provides a magnetic disk in which the
lubricating layer, a film of a lubricant containing the above
perfluorotetraol compound and perfluorodiol compound formed over
the protective layer, contains --COOH atomic groups that are
detectable by time of flight secondary ion mass spectrometry
(TOF-SIMS).
[0079] When the present inventors pursued their research still
further, they found that the effect of the present invention lay in
the relation between the --COOH atomic groups and/or --CF.sub.2COOH
atomic groups contained in the lubricating layer. That is, when the
lubricating layer of the magnetic disk of the embodiments given
further below was examined in detail by TOF-SIMS, they discovered
that --COOH atomic groups and --CF.sub.2COOH atomic groups were
present in the lubricating layer. Neither the perfluorotetraol
compound nor the perfluorodiol compound contained in the lubricant
forming the lubricating layer contained --COOH atomic groups or
--CF.sub.2COOH atomic groups. Accordingly, the effect of the
present invention was found to result from the incorporation of
--COOH atomic groups and/or --CF.sub.2COOH atomic groups into the
lubricating layer that was formed. In the embodiments of the
present invention, the use of a carbon-base protective layer and an
amorphous carbon protective layer (for example, hydrogenated carbon
protective layer) formed by plasma CVD was found to modify part of
the lubricating layer that was formed thereover, yielding carboxyl
groups. As set forth further below, a carbon-base protective layer,
particularly an amorphous carbon-base protective layer, is thought
to be related to the high affinity for alcohol-modified
perfluoropolyether compounds.
[0080] The --COOH atomic groups and --CF.sub.2COOH atomic groups
contained in the lubricating layer can both be detected by
TOF-SIMS. Since --CF.sub.2COOH atomic groups can be simultaneously
detected when detecting --COOH atomic groups, the count of
--CF.sub.2COOH atomic groups detected is included in the count of
--COOH atomic groups detected.
[0081] The present invention provides a magnetic disk having a
magnetic layer, protective layer, and lubricating layer on a
substrate, with the lubricating layer containing the above
perfluorotetraol compounds and perfluorodiol compounds, as well as
a compound having within its molecular structure --COOH atomic
groups detectable by TOF-SIMS.
[0082] Based on the information discovered by the present
inventors, the incorporation of --COOH atomic groups and/or
--CF.sub.2COOH atomic groups into the lubricating layer that is
formed is desirable to achieve the effect of the present invention.
The incorporation into the lubricating layer of a compound having
within its molecular structure --COOH atomic groups detectable by
TOF-SIMS is also desirable. In that case, the lubricating layer
contains the above perfluorotetraol compounds and perfluorodiol
compounds, as well as a compound having within its molecular
structure --COOH atomic groups. Examples of compounds having within
their molecular structure --COOH atomic groups that are detectable
by TOF-SIMS are perfluoropolyether-base compounds in which a
terminal of the main chain or a side chain has been modified into a
carboxyl group. Such a lubricating layer may be obtained, for
example, by forming a film on the protective layer of a lubricant
containing the above perfluorotetraol compounds, perfluorodiol
compounds, and compound having --COOH atomic groups in its
molecular structure.
BEST MODE OF IMPLEMENTING THE INVENTION
[0083] In the present invention, when preparing lubricant c,
lubricant a and lubricant b are desirably mixed together in a
blending proportion by weight of from 1:2 to 2:1. When the blending
proportion falls within this range, the alcohol-modified
perfluoropolyether compound contained in lubricant c is thought to
be in a particularly desirable state for solving the above-stated
problems.
[0084] In the present invention, the method of fractionation by
molecular weight is not specifically limited. For example,
molecular weight fractionation by gel permeation chromatography
(GPC) and supercritical extraction are both possible. Of these, the
use of supercritical extraction for fractionation of lubricants
alpha and beta is desirable. The use of fractionation by
supercritical extraction permits a high degree of refinement of the
lubricant. Specifically, supercritical extraction employing carbon
dioxide as eluting solvent is suitable. Molecular weight
fractionation by chromatography is preferred. Molecular weight
fractionation is also possible based on retention time.
[0085] When the pressure of the carbon dioxide is adjusted to 80 to
350 kgf/cm.sup.2 and the temperature to from 35 to 300.degree. C.,
a desirable carbon dioxide supercritical state is achieved. When
adjusted to within this range, differences in solubility due to
slight differences in molecular weight and the structure of
terminal groups can be used for precise separation by terminal
group.
[0086] When employing chromatography, carbon dioxide in a
supercritical state and containing the lubricant is made to flow
and the lubricant in the fractions eluting out of the column is
monitored. For example, monitoring can be conducted by Fourier
transform infrared spectrophotometry (FTIR) and ultraviolet
absorption. While monitoring, fractions can be obtained based on
retention time to achieve fractionation into a good molecular
weight distribution.
[0087] When preparing lubricant c, lubricants a and b may be
directly mixed, or in order to achieve a uniform mixture state,
compositions may be prepared by dispersing the two into separate
fluorine-base solvents. The compositions are then desirably mixed
and stirred, and the mixture extracted with an evaporator to obtain
lubricant c. Extraction in this manner yields a highly uniform
mixture state.
[0088] Vertrel XF, the name of a product made by Dupont Mitsui
Fluorochemicals, is desirably employed as the fluorine-base
solvent.
[0089] In the present invention, it suffices to expose the magnetic
disk to an atmosphere of 50 to 150.degree. C. following film
formation to adhere mixed lubricant c to the protective layer. This
range is lower than the decomposition temperatures of lubricants a
and b, so the breakdown of lubricant c into lower molecules is
avoidable.
[0090] In the present invention, the thickness of the lubricating
layer can be from 5 to 15 Angstroms. At below 5 Angstroms, the
lubricating properties of the lubricating layer decrease. At
greater than 15 Angstroms, fly sticking impairment sometimes occurs
and LUL durability sometimes decreases.
[0091] In the present invention, following formation of the
lubricating layer, heat treating the magnetic disk by exposing it
to an atmosphere within the above-stated temperature range has the
effect of promoting the generation of --COOH and/or --CF.sub.2COOH
atomic groups in the lubricating layer. A carbon-base protective
layer, particularly an amorphous carbon-base protective layer, has
high affinity for alcohol-modified perfluoropolyether compounds, as
set forth further below. Accordingly, forming the lubricating layer
of the present invention on a carbon-base protective layer and
subjecting it to such a heat treatment permits the suitable
generation of --COOH and/or --CF.sub.2COOH atomic groups in the
lubricating layer.
[0092] A carbon-base protective layer may be employed as the
protective layer in the present invention. An amorphous carbon
protective layer is preferred. Such a protective layer has high
affinity for alcohol-modified perfluoropolyether compounds and
yields suitable adhesion strength. The adhesion strength may be
regulated by employing a carbon protective layer of hydrogenated
carbon or nitrogenated carbon and adjusting the content of hydrogen
and/or nitrogen.
[0093] When the hydrogen content (hydrogen content in a protective
layer) is measured by hydrogen forward scattering (HFS), a level of
3 to 20 at % is desirable. When the nitrogen content (ratio of
nitrogen to carbon, N/C) is measured by X-ray photoelectric
spectroscopic analysis (XPS), a level of 4 to 12 at % is
desirable.
[0094] When employing a carbon-base protective layer in the present
invention, an amorphous carbon-base protective layer formed by
plasma CVD is desirable. An amorphous hydrogenated carbon
protective layer formed by CVD is particularly desirable. When
forming a carbon-base protective layer by plasma CVD, it suffices
to employ low unsaturation hydrogen carbide, specifically, a
straight-chain low unsaturation hydrogen carbide gas with 10 or
fewer carbon atoms, such as acetylene.
[0095] The present invention is described in greater detail below
through embodiments.
[0096] (Embodiment 1)
[0097] FIG. 1 shows a magnetic disk 10 in an implementation mode of
the present invention.
[0098] In magnetic disk 10, on a disk substrate 1 are sequentially
formed a base layer 2, magnetic layer 3, protective layer 4, and
lubricating layer 5. Lubricating layer 5 is formed out of the
lubricant (referred to as lubricant c) of the present invention.
This will be described more specifically below.
[0099] (Preparation of the Lubricant)
[0100] The method of preparing the lubricant will be described.
[0101] First, Fomblin Ztetraol (product name) made by Solvay
Solexis (referred to as lubricant alpha below) was selected and
procured as the lubricant containing the above perfluorotetraol
compound and perfluorodiol compound. A pressure column was mounted
on a supercritical fluid application device configured of a
supercritical fluid delivery device, temperature regulating device,
pressure regulating device, FTIR, and ultraviolet-visible spectrum
detector. Carbon dioxide was employed as the mobile phase in
molecular weight fractionation to fractionate the lubricant by
molecular weight based on supercritical extraction. The lubricant
obtained by fractionation was referred to as lubricant a.
[0102] Next, Fomblin Zdol (product name) made by Solvay Solexis
(referred to as lubricant beta below) was selected and procured as
the lubricant containing the above perfluorodiol compound.
Similarly, molecular weight fractionation of the lubricant by
supercritical extraction was conducted. The lubricant obtained by
fractionation was referred to as lubricant b. The details of the
supercritical extraction method are given below.
[0103] When the molecular weight distributions of lubricants a and
b that had been obtained were measured using polymethyl
methacrylates of varying molecular weight as reference substances
by gel permeation chromatography (GPC), the molecular weight
distribution of lubricant a was found to be a weight average
molecular weight (Mw) of from 3,000 to 7,000 with a molecular
weight dispersion of from 1.05 to 1.2. The molecular weight
distribution of lubricant b was found to be a weight average
molecular weight (Mw) of from 2,000 to 5,000 with a molecular
weight dispersion of from 1.05 to 1.2. The molecular weight
dispersion indicates the ratio of the weight average molecular
weight (Mw)/number average molecular weight (Mn).
[0104] A composition (referred to as composition A) was prepared by
dispersing lubricant a that had been fractionated in this manner in
Vertrel XF (product name), a fluorine-base solvent made by Dupont
Mitsui Fluorochemicals.
[0105] Similarly, a composition (referred to as composition B) was
prepared by separately dispersing lubricant b that had been
fractionated in this manner in Vertrel XF (product name) made by
Dupont Mitsui Fluorochemicals
[0106] Compositions A and B were mixed and intimately stirred to
prepare a mixed composition. Mixing was conducted in such a manner
that the blending proportion of lubricants a and b was 1:1 by
weight.
[0107] The Vertrel XF (product name), made by Dupont Mitsui
Fluorochemicals, was removed from the mixed composition with an
evaporator, and a lubricant was extracted (referred to as lubricant
c below).
[0108] Preparing the above lubricant in a clean room kept the
purity of lubricant c high. The cleanliness class of the atmosphere
of the clean room that was employed exceeded cleanliness class 6
specified by Japan Industrial Standard (JIS) B9920 or ISO
(14644-1), or exceeded cleanliness class 1000 (Federal Standard:
FED-STD-209D).
[0109] (Manufacturing of a Magnetic Disk)
[0110] A 2.5-inch chemically reinforced glass disk (outer diameter
65 mm, inner diameter 20 mm, disk thickness 0.635 mm) made of
alumina silicate glass was procured for use as disk substrate
1.
[0111] On this disk substrate were sequentially formed by DC
magnetron sputtering a base layer 2 and a magnetic layer 3.
[0112] Base layer 2 was prepared by forming over a first base layer
comprised of a thin AlRu alloy film a second base layer comprised
of a thin CrW alloy film. Magnetic layer 3 was a thin CoCrPtB alloy
film.
[0113] Next, plasma CVD was employed to form a protective layer 4
(60 Angstroms in thickness) comprised of amorphous diamond-like
carbon. When forming the film, low straight-chain hydrogen carbide
gas was employed.
[0114] When protective layer 4 was analyzed by HFS, it was found to
contain 15 at % of hydrogen.
[0115] Next, previously prepared lubricant c was coated by dipping
to form lubricating layer 5.
[0116] After film formation, magnetic disk 10 was heated in an oven
to 100.degree. C. to adhere lubricant c to protective layer 4.
Heating was conducted for one hour. Measurement by FTIR revealed
lubricating layer 5 to be 10 Angstroms in thickness.
[0117] (Evaluation of the Magnetic Disk)
[0118] An LUL durability test was conducted to determine the LUL
(load-unload) durability of the magnetic disk 10 obtained.
[0119] An LUL-system hard disk drive (HDD) (rotating at 5,400 rpm)
was procured and magnetic disk 10 was loaded with a magnetic head
having a flying height level of 10 nm. The magnetic head had an
NPAB slider on which was mounted a reproduction element in the form
of a magnetoresistive element (GMR element). The shield element was
made of FeNi-base permalloy. LUL operations were repeatedly
conducted with this LUL-system HDD and the number of LUL operations
that magnetic disk 10 lasted before failure occurred was
counted.
[0120] As a result, it was found that magnetic disk 10 of the
present embodiment lasted 800,000 LUL operations without failing.
It is said that about 10 years of use is required to exceed 400,000
LUL operations under a normal HDD use environment. Thus, magnetic
disk 10 of the present invention was highly reliable.
[0121] No fly-sticking impairment occurred with any of the HDDs
that were tested.
[0122] Detailed examinations of the surface of the magnetic head
following LUL durability testing were conducted by optical
microscope and electron microscope. However, no scoring or
corrosion was found. Nor was any transfer of lubricant to the
magnetic head observed.
[0123] (Embodiments 2 and 3)
[0124] In Embodiment 2, the blending proportion of compositions A
and B was varied to achieve a weight ratio of 1:2 of lubricant a to
lubricant b.
[0125] In Embodiment 3, the mixing ratio of compositions A and B
was varied to achieve a blending proportion by weight of 2:1 of
lubricant a to lubricant b. These exceptions aside, these
embodiments were identical to Embodiment 1.
[0126] When LUL durability testing was conducted in the same manner
as in Embodiment 1, both Embodiments 2 and 3 achieved the same good
results as Embodiment 1.
[0127] A detailed analysis of the lubricating layers of the
magnetic disks of each of Embodiments 1 through 3 by TOF-SIMS
revealed that the magnetic disks of all of the embodiments
contained --COOH atomic groups and --CF.sub.2COOH atomic groups in
the lubricating layer. These atomic groups were not contained in
either the above perfluorotetraol compound or the above
perfluorodiol compound; nor were they contained in lubricant alpha,
lubricant beta, lubricant a, lubricant b, or lubricant c.
Accordingly, they were thought to be atomic groups that had been
generated in the lubricating layer after the formation of the film
of lubricant c on the protective layer.
[0128] Further, FTIR analysis of the lubricating layer revealed the
presence of an absorption band at 1730.+-.10 cm.sup.-1 in the
infrared absorption spectrum.
[0129] A magnetic disk was prepared by forming by the same method
as in Embodiment 1 a lubricating layer 5 over a hydrogenated carbon
protective layer formed by sputtering, but without heat treatment
following the formation of lubricating layer 5. Analysis of the
lubricating layer by TOF-SIMS revealed a quantity of --COOH atomic
groups and --CF.sub.2COOH atoms groups that was at about the limit
of detection by TOF-SIMS. When this magnetic disk was subjected to
LUL durability testing, the number of LUL operations exceeded
400,000 and no fly-sticking impairment was found. However, some
transfer of lubricant to the magnetic head was observed. Thus, the
magnetic disk of Embodiment 1, in which --COOH atomic groups and/or
--CF.sub.2COOH atomic groups were generated in the lubricating
layer, was determined to be more reliable.
COMPARATIVE EXAMPLES 1 AND 2
[0130] In Comparative Example 1, lubricant alpha was applied over
protective layer 4 without fractionation. In Comparative Example 2,
lubricant beta was applied over protective layer 4 without
fractionation.
[0131] When LUL durability testing was conducted in the same manner
as in Embodiment 1, Comparative Example 1 failed at 400,000 LUL
operations. Further, fly-sticking impairment occurred in 50 percent
of the HDDs tested. Comparative Example 2 failed at 200,000 LUL
operations. Further, fly-sticking impairment occurred in 90 percent
of the HDDs tested.
[0132] When the magnetic heads of the HDDs of Comparative Examples
1 and 2 were removed and examined after testing, transfer of
lubricant to the ABS surface and NPAB pocket portion of the
magnetic heads was observed.
COMPARATIVE EXAMPLE 3
[0133] In Comparative Example 3, lubricants alpha and beta were
mixed in a weight ratio of 1:1 to prepare the lubricant that was
coated on the protective layer.
[0134] When LUL durability testing was conducted in the same manner
as in Embodiment 1, Comparative Example 3 failed at 400,000 LUL
operations. Further, fly-sticking impairment was generated in 70
percent of the HDDS employed in the testing. When the magnetic head
of the HDD was removed and examined after testing, transfer of
lubricant to the ABS surface and NPAB pocket portion of the
magnetic head was observed.
[0135] When the lubricating layer of the magnetic disk of
Comparative Example 2 was analyzed in detail by TOF-SIMS,
absolutely no --COOH atomic groups or --CF.sub.2COOH atomic groups
were detected in the lubricating layer. Thus, the magnetic disk of
the embodiments in which --COOH and/or --CF.sub.2COOH atomic groups
were generated in the lubricating layer were determined to be more
reliable.
[0136] In the present invention, a lubricant alpha (for example,
Fomblin Ztetraol, the name of a product made by Solvay Solexis) is
fractionated by molecular weight to obtain a lubricant a with a
weight average molecular weight (Mw) of from 3,000 to 7,000 and a
molecular weight dispersion of less than or equal to 1.2; a
lubricant beta (for example, Fomblin Zdol, the name of a product
made by Solvay Solexis) is fractionated by molecular weight to
obtained a lubricant b with a weight average molecular weight (Mw)
of from 2,000 to 5,000 and a molecular weight dispersion of less
than or equal to 1.2; and lubricants a and b are mixed to obtain a
lubricant c which is employed to form a lubricating layer. Thus,
the present invention provides a magnetic disk in which
fly-sticking impairment and corrosion impairment are prevented that
is particularly suited to use in LUL-system magnetic disk
devices.
[0137] Further, the incorporation of --COOH atomic groups
detectable by TOF-SIMS into the lubricating layer yields an
extremely reliable magnetic disk particularly suited to LUL
durability.
[0138] The present disclosure relates to subject matter contained
in Japanese Patent Application Nos. 2003-96820, filed on Mar. 31,
2003, and 2003-361982, filed on Oct. 22, 2003, the contents of both
are herein expressly incorporated by reference in their
entireties.
* * * * *